Hollow sphere structure of metal-containing tungsten carbide, method for manufacturing the same, method for manufacturing film

ABSTRACT

A hollow sphere structure of metal-containing tungsten carbide is provided, which includes a porous shell of metal-containing metal carbide surrounding a hollow core. The hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, and the porous shell has a thickness of 0.1 micrometers to 12 micrometers. The metal is cobalt, nickel, or a combination thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority from, Taiwan Application Serial Number 105141021, filed on Dec. 12, 2016, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The technical field relates to a hollow sphere structure of metal-containing tungsten carbide, a method for manufacturing the same, and an application thereof.

BACKGROUND

Tungsten carbide exhibits abrasion resistance, and therefore is often used as a function material in cutting tools, spray guns, casting molds, and other abrasion-resistant components. An important topic in the development of modern tungsten carbide materials is how to enhance its inherently abrasion resistant efficiency so that it can be further applied in petrochemicals, steel, and other industries. The lifespan of conventional micro-scale particles of tungsten carbide material is short due to the layered particles easily becoming delaminated during use. However, either nano-scale or sub-micro-scale tungsten carbide material is less brittle at room temperature (which is equal to improved toughness), thus inner stress in the film of the tungsten carbide are also decreased. Simultaneously, a film formed from either nano-scale or sub-micro-scale tungsten carbide particles is free of layered structures, and the film will not be delaminated during use, thereby increasing the lifespan of the film. However, the nano-scale or sub-microscale tungsten carbide particles have poor flowability and low compacted density, and it is difficult to directly compact them to from a body of high density. The body should be sintered at high temperature for a long period to increase the density of the sintered product, but the above sintering process may induce grain growth in the product. As such, the product will lose its nano-scale or sub-microscale grain in its inner structure.

Accordingly, a novel tungsten carbide material structure is called for.

SUMMARY

One embodiment of the disclosure provides a hollow sphere structure of metal-containing tungsten carbide, comprising: a porous shell of metal-containing tungsten carbide surrounding a hollow core, wherein the hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, the porous shell has a thickness of 0.1 micrometers to 12 micrometers, and the metal is cobalt, nickel, or a combination thereof.

One embodiment of the disclosure provides a method of forming a hollow sphere structure of metal-containing tungsten carbide, comprising: wet-dispersing a plurality of metal-containing tungsten carbide particles to form slurry; and spray drying the slurry to connect the metal-containing tungsten carbide particles for forming the hollow sphere structure of metal-containing tungsten carbide by a spray dryer, wherein the hollow sphere structure of metal-containing tungsten carbide includes a porous shell of metal-containing tungsten carbide surrounding a hollow core, wherein the hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, the porous shell has a thickness of 0.1 micrometers to 12 micrometers, and the metal is cobalt, nickel, or a combination thereof.

One embodiment of the disclosure provides a method for manufacturing a film, comprising: thermal spraying a hollow sphere structure of metal-containing tungsten carbide to form a metal-containing tungsten carbide film on a substrate, wherein the hollow sphere structure of metal-containing tungsten carbide includes a porous shell of metal-containing tungsten carbide surrounding a hollow core, wherein the hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, the porous shell has a thickness of 0.1 micrometers to 12 micrometers, and the metal is cobalt, nickel, or a combination thereof.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 shows a hollow sphere structure of metal-containing tungsten carbide in one embodiment;

FIGS. 2A and 2B show SEM photographs of tungsten carbide particles in one embodiment;

FIGS. 3A to 3D show SEM photographs of an agglomerated hollow sphere structure in one embodiment;

FIGS. 4A and 4B show SEM photographs of a sintered hollow sphere structure in one embodiment;

FIG. 5 shows XRD spectra of the initial tungsten carbide particles and the agglomerated hollow sphere structure in one embodiment;

FIGS. 6A to 6C show SEM photographs of a film formed by thermal spraying the hollow sphere structure in one embodiment;

FIGS. 7A and 7B show SEM photographs of a sintered hollow sphere structure in one embodiment;

FIGS. 8A and 8B show SEM photographs of a sintered hollow sphere structure in one embodiment;

FIGS. 9A and 9B show SEM photographs of a sintered hollow sphere structure in one embodiment;

FIGS. 10A to 10D show SEM photographs of commercially available cobalt-containing tungsten carbide particles #1 in one embodiment;

FIGS. 11A to 11D show SEM photographs of commercially available cobalt-containing tungsten carbide particles #2 in one embodiment;

FIG. 12A to 12C show SEM photographs of a film formed by thermal spraying the cobalt-containing tungsten carbide particles #1 in one embodiment; and

FIG. 13A to 13C show SEM photographs of a film formed by thermal spraying the cobalt-containing tungsten carbide particles #2 in one embodiment;

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown schematically in order to simplify the drawing.

One embodiment of the disclosure provides a method of forming a hollow sphere structure of metal-containing tungsten carbide. Metal is formed on tungsten carbide particles to obtain metal-containing tungsten carbide particles. The metal can be cobalt, nickel, or a combination thereof. In one embodiment, the metal and the tungsten carbide of the metal-containing tungsten carbide particles have a weight ratio of 10:90 to 14:86 (e.g. 12:88).

In one embodiment, the metal-containing tungsten carbide particles before a process (e.g. ball-milling) have an original diameter of 0.2 micrometers to 0.8 micrometers. The metal-containing tungsten carbide particles after the process (e.g. ball-milling) have an original diameter of 0.05 micrometers to 0.6 micrometers. Processed metal-containing tungsten carbide particles that are too small may cause an agglomerated hollow sphere structure (formed in subsequent steps) to break easily during sintering. Processed metal-containing tungsten carbide particles that are too big cannot be agglomerated to form the hollow sphere structure. In one embodiment, the processed metal-containing tungsten carbide particles include two grades: Grade I particles and Grade II particles have different diameters. For example, Grade I particles have a diameter of 0.05 micrometers to 0.2 micrometers, and Grade II particles have a diameter of 0.2 micrometers to 0.6 micrometers. Compared to the hollow sphere structure formed of the metal-containing tungsten carbide particles with a single diameter (e.g. only Grade I particles or Grade II particles), the hollow sphere structure formed of the combination of Grade I particles and Grade II particles is not more easy to result in the bursting of agglomerated particles after consequence sintering process. In one embodiment, Grade I particles and Grade II particles have a weight ratio of 0.08:1 to 100:1. In conventional art, it is difficult to directly aggregate Grade I (or Grade II) primary nano-scaled (or submicron-scaled) particles to form micro-scaled secondary particles. Too high a ratio of Grade II particles (or Grade II particles) will be similar to the effect of utilizing the particles of a single diameter.

Subsequently, the metal-containing tungsten carbide particles are wet-dispersed to form slurry. In one embodiment, 1 part by weight of the metal-containing tungsten carbide particles, 0.007 to 0.1 parts by weight of the polyvinyl alcohol (PVA), 0.5 to 5 parts by weight of water, and 1 to 10 parts by weight of alumina or zirconia mill balls (having a diameter of 4 mm to 12 mm) are put into a ball-milling machine to be wet ball-milled at 200 rpm to 500 rpm for 1 hour to 4 hours, thereby obtaining slurry.

The slurry is fed into a spray drier (YS-SD-2, commercially available from Inora) at a feeding rate of 10 rpm to 20 rpm, and then stirred in the spray dryer at 150 rpm to 200 rpm. The slurry was then sprayed through a nozzle at a pressure of 0.1 bar to 1 bar, and then dried with hot air of 150° C. to 200° C. for agglomeration. The pressure difference of the nozzle was between −10 Pa to −20 Pa, and the air hammer frequency was 1 to 3 Hz. After the spray drying, the metal-containing tungsten carbide particles 11 will be connected to form the hollow sphere structure 10, as shown in FIG. 1. The hollow sphere structure 10 of the metal-containing tungsten carbide includes a porous shell 13 surrounding a hollow core 15. The hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, and its porous shell has a thickness of 0.1 micrometers to 12 micrometers. Too thin a shell 13 will be delaminated and spread. Too thick a shell 13 will form a solid core structure. In one embodiment, the porous shell 13 includes a plurality of pores with a diameter of 0.3 micrometers to 2 micrometers. Pores that are too small may cause the hollow sphere structure break easily during sintering. It is difficult to form a hollow sphere structure with pores that are too big.

In one embodiment, the hollow sphere structure can be directly thermal sprayed to form a metal-containing tungsten carbide film on a substrate. For example, the hollow sphere structure of cobalt-containing tungsten carbide can be thermal sprayed by a mixture gas of propane, oxygen, and nitrogen to form the cobalt-containing tungsten carbide film on the substrate. In one embodiment, the propane pressure is 3 bar to 10 bar, the oxygen pressure is 2 bar to 10 bar, and the nitrogen pressure is 1 bar to 10 bar. Compared to thermal spraying a solid core of metal-containing tungsten carbide, thermal spraying the hollow sphere structure of metal-containing tungsten carbide may form a denser film with fewer pores and smaller tungsten carbide particles.

Alternatively, the hollow sphere structure of metal-containing tungsten carbide can be optionally sintered to form an irregular worm-shaped structure or a multi-edge angle structure on an inner surface and an outer surface of the porous shell. In one embodiment, the sintering process is performed at a temperature of 1000° C. to 1200° C. under an atmosphere of nitrogen for a period of 10 minutes to 30 minutes. In one embodiment, the irregular worm-shaped structure has a length×width of about 0.3 micrometers×1.7 micrometers to 0.3 micrometers×0.7 micrometers, and the multi-edge angle structure has a length×width of about 0.3 micrometers×2.6 micrometers to 0.5 micrometers×1.8 micrometers. In addition, the connected metal-containing tungsten carbide particles in the porous shell have a strip-shaped nanostructure with a length×width of about 130 nm to 500 nm×13 nm to 44 nm. The metal-containing tungsten carbide particles can be further connected by the sintering step, thereby avoiding the particles becoming delaminated from the hollow sphere structure.

Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The inventive concept may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout.

EXAMPLES Example 1

First, tungsten carbide particles (Kallex) with a diameter of 0.8 micrometers were provided. The SEM photographs of the tungsten carbide particles are shown in FIGS. 2A and 2B. In FIG. 2B, the tungsten carbide particles in region A had irregular shapes, and the tungsten carbide particles in region B had slightly regular cleaved crystal face structures. Subsequently, cobalt was formed on the tungsten carbide particles. 1 part by weight of the cobalt-containing tungsten carbide, 0.02 parts by weight of polyvinyl alcohol (PVA), 1.5 parts by weight of water, 3.3 parts by weight of alumina mill balls (having a diameter of 8 mm) were then mixed and put into a ball-milling machine to be wet ball-milled at 327 rpm for 4 hours, thereby obtaining slurry. After the process and treatment (e.g. ball milling), the cobalt-containing tungsten carbide particles in the slurry had a diameter of 0.05 micrometers to 0.6 micrometers.

The slurry was fed into a spray dryer (YS-SD-2, commercially available from Inora) at a feeding rate of 20 rpm, and the slurry stirred at 150 rpm during the spray drying process. The slurry was then sprayed through a nozzle at a pressure of 1 bar, and then dried with hot air of 150° C. to 200° C. to vaporize the moisture thereof, thereby forming a group of agglomerated particles. The pressure difference of the nozzle was between −10 Pa to −20 Pa, and the air hammer frequency was 1 to 3 Hz. The group of agglomerated particles was a hollow sphere structure, and SEM photographs thereof are shown in FIGS. 3A to 3C. An SEM photograph of a cross-section of the hollow sphere structure is shown in FIG. 3D, and a shell of the hollow sphere structure had a thickness of about 11.5 micrometers. The hollow sphere structure had a porous shell surrounding a hollow core, and the porous shell was composed of a plurality of connected cobalt-containing tungsten carbide particles. The hollow sphere structure was analyzed by energy dispersive X-ray spectrometry (EDS) to determine its elements: C (13.8 wt %), Co (13.13 wt %), and W (73.07 wt %).

The hollow sphere structure was put under a low pressure environment (1×10⁻² torr to 3×10⁻² torr), and nitrogen with a flow rate of 10 liters/minute to 30 liters/minute was then introduced into the environment. The hollow sphere structure was then heated to and sintered at 1000° C. for 10 minutes. SEM photographs of the sintered hollow sphere structure are shown in FIGS. 4A and 4B, in which the inner surface and the outer surface of the porous shell had an irregular worm-shaped structure (Region A, having a length of about 0.3 micrometers to 2 micrometers) and a multi-edge angle structure (Region B, having a length of about 0.8 micrometers to 2 micrometers). In addition, the connected cobalt-containing tungsten carbide particles in the porous shell had strip-shaped nanostructures (Regions C and D). The nanostructure in region C had a length×width of about 131 nm×12.5 nm, and the nanostructure in region D had a length×width of about 500 nm×43.7 nm. FIG. 5 shows XRD spectra of the initial tungsten carbide particles (without cobalt formed thereon) and the agglomerated hollow sphere structure, and it determined that the major phase of the hollow sphere structure was tungsten carbide crystal phase.

Subsequently, the hollow sphere structure was thermal sprayed by a mixture gas of 5.2 bar of propane, 8 bar of oxygen, and 5 bar of nitrogen to form a cobalt-containing tungsten carbide film with a thickness of 100 micrometers on a substrate. The thermal spray equipment was CDS R-75C (commercially available from Struers), the feed rate was 17 rpm, the feed inlet and the substrate had a distance of 203 mm therebetween, and the a movement rate of nozzle was 1200 mm/second. FIGS. 6A to 6C show SEM photographs of a cross-section of the film. As shown in FIG. 6A, the film had very few pores. As shown in FIG. 6C, most of the tungsten carbide particles (long-shaped particles) in the film were round-angled particles, which were suitable for used in knives (due to lowering the cleave possibility caused from stress concentration). The film was quantitatively analyzed by EDS to determine its content: C (5.54 wt %), O (0.84 wt %), Co (10.95 wt %), and W (82.67 wt %), which was close to the ideal atomic ratios (e.g. C (5.5 wt %), Co (11 wt %), and W (83.5 wt %)).

Example 2

Example 2 was similar to Example 1, with the difference being that the initial tungsten carbide particles had a diameter of 0.2 micrometers. The other processing conditions of forming the cobalt on the tungsten carbide particles, agglomerating the particles to form the hollow sphere structure, and sintering the hollow sphere structure were similar to those in Example 1, and the related descriptions are omitted here. FIGS. 7A and 7B show SEM photographs of the sintered hollow sphere structure, in which the hollow sphere structure was partially broken after the sintering process.

Example 3

Example 3 was similar to Example 1, with the difference being that the initial tungsten carbide particles included 25 wt % of particles with a diameter of 0.2 micrometers and 75 wt % of particles with a diameter of 0.8 micrometers. The other processing conditions of forming the cobalt on the tungsten carbide particles, agglomerating the particles to form the hollow sphere structure, and sintering the hollow sphere structure were similar to those in Example 1, and the related descriptions are omitted here. FIGS. 8A and 8B show SEM photographs of the sintered hollow sphere structure, in which more pores were formed in the shell of the hollow sphere structure, such that the hollow sphere structure was not broken after the sintering process.

Example 4

Example 4 was similar to Example 1, with the difference being that the initial tungsten carbide particles included 50 wt % of particles with a diameter of 0.2 micrometers and 50 wt % of particles with a diameter of 0.8 micrometers. The other processing conditions of forming the cobalt on the tungsten carbide particles, agglomerating the particles to form the hollow sphere structure, and sintering the hollow sphere structure were similar to those in Example 1, and the related descriptions are omitted here. FIGS. 9A and 9B show SEM photographs of the sintered hollow sphere structure, in which more pores were formed in the shell of the hollow sphere structure, such that the hollow sphere structure was not broken after the sintering process.

Comparative Example 1

Sources, cobalt content, and particle diameter of several commercially available cobalt-containing tungsten carbide particles are tabulated in Table 1.

TABLE 1 Cobalt Particle No. Manufacture content (%) diameter (μm) 1 Sulzer 12 15-45 Metco 2 NEI 12 <44

FIGS. 10A to 10B show SEM photographs of cobalt-containing tungsten carbide particles #1, and FIG. 10D shows an SEM photograph of a cross-section of the cobalt-containing tungsten carbide particles #1 (Solid core structure). The cobalt-containing tungsten carbide particles #1 were thermal sprayed by a mixture gas of 5.2 bar of propane, 8 bar of oxygen, and 5 bar of nitrogen to form a cobalt-containing tungsten carbide film with a thickness of 100 micrometers on a substrate. The thermal spray equipment and conditions were similar to those in Example 1, and the related descriptions are omitted here. FIGS. 12A to 12C show SEM photographs of a cross-section of the film. As shown in FIG. 12A, the film had obvious pores. As shown in FIG. 12C, the tungsten carbide particles in the film had the shape of an eggshell fracture and a diameter of 367 nm to 1067 nm. In other words, the film had a cracked grain of tungsten carbide.

The cobalt-containing tungsten carbide particles #2 were thermal sprayed by a mixture gas of 5.2 bar of propane, 8 bar of oxygen, and 5 bar of nitrogen to form a cobalt-containing tungsten carbide film with a thickness of 100 micrometers on a substrate. The thermal spray equipment and conditions were similar to those in Example 1, and the related descriptions are omitted here. FIGS. 13A to 13C show SEM photographs of a cross-section of the film. The film had many pores and cracks. As shown in FIG. 13C, the film had many brighter large grains of tungsten carbide with a diameter of 267 nm to 2000 nm. The grains also had more sharp angles. Therefore, the film had more cracks.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed methods and materials. It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalents. 

What is claimed is:
 1. A hollow sphere structure of metal-containing tungsten carbide, comprising: a porous shell of metal-containing tungsten carbide surrounding a hollow core, wherein the hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, the porous shell has a thickness of 0.1 micrometers to 12 micrometers, and the metal is cobalt, nickel, or a combination thereof.
 2. The hollow sphere structure of metal-containing tungsten carbide as claimed in claim 1, wherein an inner surface or an outer surface of the porous shell has a worm-shaped structure or a multi-edge angle structure.
 3. The hollow sphere structure of metal-containing tungsten carbide as claimed in claim 1, wherein the porous shell has a plurality of pores, and the pores have a diameter of 0.3 micrometers to 2 micrometers.
 4. The hollow sphere structure of metal-containing tungsten carbide as claimed in claim 1, wherein the porous shell is formed of a plurality of connected metal-containing tungsten carbide particles.
 5. The hollow sphere structure of metal-containing tungsten carbide as claimed in claim 4, wherein the metal-containing tungsten carbide particles have a metal formed on tungsten carbide particles.
 6. The hollow sphere structure of metal-containing tungsten carbide as claimed in claim 4, wherein the metal-containing tungsten carbide particles have a diameter of 0.05 micrometers to 0.6 micrometers.
 7. The hollow sphere structure of metal-containing tungsten carbide as claimed in claim 4, wherein the metal and the tungsten carbide particles of the metal-containing tungsten carbide particles have a weight ratio of 10:90 to 14:86.
 8. A method of forming a hollow sphere structure of metal-containing tungsten carbide, comprising: wet-dispersing a plurality of metal-containing tungsten carbide particles to form slurry; and spray drying the slurry to connect the metal-containing tungsten carbide particles for forming the hollow sphere structure of metal-containing tungsten carbide, wherein the hollow sphere structure of metal-containing tungsten carbide includes a porous shell of metal-containing tungsten carbide surrounding a hollow core, wherein the hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, the porous shell has a thickness of 0.1 micrometers to 12 micrometers, and the metal is cobalt, nickel, or a combination thereof.
 9. The method as claimed in claim 8, wherein the porous shell has a plurality of pores, and the pores have a diameter of 0.3 micrometers to 2 micrometers.
 10. The method as claimed in claim 8, wherein the metal-containing tungsten carbide particles have a metal formed on tungsten carbide particles.
 11. The method as claimed in claim 8, wherein the metal-containing tungsten carbide particles have a diameter of 0.05 micrometers to 0.6 micrometers in the slurry.
 12. The method as claimed in claim 8, wherein the metal-containing tungsten carbide particles after spray drying include two grades, wherein Grade I particles have a diameter of 0.05 micrometers to 0.2 micrometers and Grade II particles have a diameter of 0.2 micrometers to 0.6 micrometers.
 13. The method as claimed in claim 12, wherein Grade I particles and Grade II particles have a weight ratio of 0.08 to
 1. 14. The method as claimed in claim 8, wherein the metal and the tungsten carbide particles of the metal-containing tungsten carbide particles have a weight ratio of 10:90 to 14:86.
 15. The method as claimed in claim 8, further sintering the hollow sphere structure of metal-containing tungsten carbide to form a worm-shaped structure or a multi-edge angle structure at an inner surface or an outer surface of the porous shell.
 16. A method for manufacturing a film, comprising: thermal spraying a hollow sphere structure of metal-containing tungsten carbide to form a metal-containing tungsten carbide film on a substrate, wherein the hollow sphere structure of metal-containing tungsten carbide includes a porous shell of metal-containing tungsten carbide surrounding a hollow core, wherein the hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, the porous shell has a thickness of 0.1 micrometers to 12 micrometers, and the metal is cobalt, nickel, or a combination thereof. 